SYSML21 — SenderReceiverPart definition is unclear; an example of multiple uses of the same relations in the same definition

It is unclear how to handle multiple uses of the same relations in the same keyword definition

SenderReceiverPart : SendActionUsage =
'via' ownedRelationship += NodeParameterMember
( 'to' ownedRelationship += NodeParameterMember )?

I have not seen a specification of how to handle these relationship specifications from the point of view of data presentation.
I assume that for the first line I would follow the ownedRelationship from the SendActionUsage element. This makes sense with respect to NodeParameterMember which then navigates to the related element. Fine.
So what about the next line? That appears to do exactly the same with different leading text and is indicated as optional.
Then we appear to have a specification of what to do if there is no related element. EmptyParameterMember appears to specify a relationship which has no specified target. EmptyUsage = {} but not '{}' so there appears to be nothing to present.
Then we have the final line which is again a repeat of the former but specifying NodeParameterMember.